In general, the interruption of the rake face of cutting inserts with laterally spaced depressions in the chip path from the cutting edge has been appreciated for its ability to render chips removed from ductile work material more readily breakable. The effect of properly placed depressions is to produce longitudinal ridges in the chip while it remains in a somewhat plastic state due to the high temperature produced by the velocity of the forceable shearing of the chip from the workpiece. The ridges, in turn, stiffen the chip against bending and hasten the attainment of a sufficiently high level of bending stress or strain at a point in the chip remote from the cutting site to cause it to break off.
The effect varies with the flow properties of the material, and with the cutting speed and feed rate, which influence the strain rate and heat generated in the chip as well as determining its thickness.
The object of this invention is the provision of an insert, suitable for use in drills and other applications, that will break chips of ductile materials into short lengths over a practical working range of feed rates and chip thicknesses.